Ocean Invertebrates: Sponges & Cnidarians

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  • 0:04 Marine Invertebrates
  • 0:34 Sponges
  • 1:52 Cnidarians
  • 3:08 Lesson Summary
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Lesson Transcript
Instructor: Sarah Cobarrubias
While some may call them simple, sponges and cnidarians have some amazing abilities. This lesson tells the story these ocean invertebrates, ranging from sponges to coral to jellyfish.

Marine Invertebrates

At least 97 percent of the world's animal life is made up of invertebrates, which are animals lacking a backbone that protects the spinal column. So, it's probably no surprise that many of them live in marine environments. After all, being supported by water means that there is less need for the postural support that a backbone provides.

In fact, some of the largest animals in the ocean, such as the giant squid, are invertebrates. But right now, we're going to focus on two much smaller marine invertebrates: sponges and cnidarians.


Sponges are aquatic invertebrates with squishy, porous bodies. They can be found on the seafloor and atop rocks. They are among the oldest species on Earth, and scientists have discovered some sponge fossils older than dinosaurs. One reason for the species' survival is that they can grow and thrive in some of the most hostile conditions, ranging from polar depths to caves that receive little light or nourishment.

Sponges are known for their famous shape and their porous texture. The pores allow the sponge to work as a sort of filter. It takes in the water and feeds on the tiny microorganisms that come with it. That's why these creatures were once used as household sponges - the kind you use to wash your dishes. Today, we usually spare the underwater sponges and instead use man-made sponges for household cleaning.

As relatively simple creatures, sponges can produce with or without a mate. In fact, they have a variety of methods of reproduction. Some sponges will reproduce through a process known as regeneration, which is when it releases part of itself and that fragment of the sponge turns into a new sponge entirely. The lost fragment on the original sponge grows back. Some sponges may release larvae that swim about looking for a suitable place to spend a few thousand years. That's right, some sponges can live for thousands of years.


While most people are familiar with sponges, they may be left scratching their heads at the mention of cnidarians, a phylum of aquatic invertebrates that includes everything from coral to jellyfish. Like sponges, cnidarians are believed to be one of the first multicellular forms of life on Earth. There are more than 9,000 species of cnidarians, and they have different structures, aquatic habitats, and ways of acquiring food. However, most cnidarians, like their friends the sponges, feed on microorganisms. Some filter water through their pores to collect food. Others, like jellyfish, use spiny barbs that contain venom to disable their prey.

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